This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
The Voice over Internet Protocol (VOIP) technology is a communication technology that enables voice calls using digital data signals. At a user's gateway equipment, the data signals are used by a VOIP unit to provide a VOIP call to the user. The data signals may be transferred through a separate IP network or in combination with analog voice signals through an existing telephone network, such as the Public Switched Telephone Network (PSTN). The PSTN transfers the analog voice signals using a low frequency band of a PSTN cable and digital data signals using a high frequency band of the cable. At the user's end, the low-band and high-band signals are separated by a splitter into the voice signals and the data signals, which are fed to the gateway equipment to provide a conventional telephone call and the VOIP call, respectively.
FIG. 1 schematically shows a gateway equipment 100 and its connection to a PSTN network and a user's telephone set. As shown in the figure, the gateway equipment 100 comprises a Foreign Exchange Station (FXS) port 110, a Foreign Exchange Office (FXO) port 120, a VOIP unit 130, and a Digital Subscriber Line (DSL) port 140. The FXS port 110 is configured to be connected to the telephone set 150. The FXO port 120 and the DSL port 140 are configured to be connected to a splitter 150, which is configured to separate signals from the PSTN network 170 into low-band voice signals and high-band data signals and feed them into the FXO port 120 and the DSL port 140, respectively. The VOIP unit 130 is configured to enable a VOIP call using the data signals from the DSL port 140. The gateway equipment 100 also comprises a switch device 180 configured to switch between a connection between the FXS port 110 and the FXO port 120 and a connection between the FXS port 110 and the VOIP unit 130. The switch device 180 connects the FXS port 110 to the VOIP unit 130 to enable the VOIP call when the gateway equipment 100 is power on. However, when the gateway equipment 100 is power down due to, e.g., the user manually turning off the gateway equipment 100 or accidental blackout of electricity system, the switch device 180 switches to the connection between the FXS port 110 and the FXO port 120. In this way, the uncompleted VOIP call can be continued by the conventional telephone call using the voice signals from the FXO port 120.
It should be noted that, in case where the data signals are provided from a separate IP network, the splitter 160 can be omitted so that the FXO port 120 communicates with the PSTN network while the DSL port 140 communicates with the IP network.
FIG. 2 schematically shows a typical structure of an electromagnetic switch device 200 for use as the above-described switch device 180. As shown in the figure, the switch device 200 comprises a switch 210 and an inductive coil 220, which is actuated by an onboard supply 230 under control of a control signal 240. The control signal 240 may be provided from a control unit (not shown), e.g., a CPU of the gateway equipment 100. When the gateway equipment 100 is power on, current runs through the coil 220 so that the switch 210 is pushed up to connect the FXS port 110 to the VOIP unit 130 by connecting a TIP pin FXS_TIP and a Ring pin FXS_RING of the FXS port 110 to a TIP pin VOIP_TIP and a Ring pin VOIP_RING of the VOIP unit 130, respectively. Thus, a VOIP call is enabled using the digital data signals. When the gateway equipment 100 is power down, the switch 210 falls down under the effect of gravity to connect the TIP pin FXS_TIP and the Ring pin FXS_RING of the FXS port 110 to a TIP pin FXO_TIP and a Ring pin FXO_RING of the FXO port 120, respectively. In this way, the call can be continued using the voice signals from the FXO port 120.
As the switch device switches mechanically between the VOIP unit and the FXO port, there may be audible noise and the lifetime of the switch device may be limited. Furthermore, there is a relatively strict requirement on mechanical contacting stability of the switch device to ensure a high-quality communication, which may result in high manufacture cost thereof. Moreover, the electromagnetic switch is typically large in size, causing a large dimension and a complex layout of the gateway equipment.